console.log(buy_water)

var buy_water = function(money) {
    switch (money) {
        case 2:
            console.log('农夫山泉');
            break;

        case 3.5:
            console.log('冰红茶');
            break;

        case 5:
            console.log('红牛')
            break;

        default:

            console.log('水')
    }
}

buy_water(15)

console.log(buy_water)